High speed silver chloroiodide emulsions

ABSTRACT

In a process for the preparation of a silver halide photographic emulsion containing a major proportion of chloride, about 0.1 mole to about 5 mole percent of iodide and up to about 10 mole percent of bromide comprising precipitating said silver halide in the presence of a hydrophilic colloid, the improvement which comprises precipitating said silver halide into a medium having a pH in the range 5-9 and a pAg of at least about 7.8 by adding to the precipitation mixture, no later than at the end of said precipitation, a weak solvent for silver halide selected from the group consisting of ammonium chloride, ammonium nitrate and magnesium chloride in a quantity in stoichiometric excess with respect to the quantity of alkali metal chloride necessary for the precipitation of the silver halide, this excess being between 4 moles and 180 moles per 100 moles of formed silver halide.

United States Patent [1 1 Perignon [451 Jan. 8, 1974 Philippe Perignon, Vincennes, France [75] Inventor:

[73] Assignee: Eastman Kodak Company,

Rochester, NY,

[22] Filed: Nov. 3, 1971 [2]] Appl. No.: 195,465

[30] Foreign Application Priority Data Nov. 13, 1970 France 70.40564 [52] [1.5. CI. 96/94, 96/114.7 [51] G03 l/02 [58] Field of Search 96/94, 114.7

[56] References Cited UNITED STATES PATENTS 2,401,051 5/1946 Crouse 96/94 2,618,556 11/1952 Hewitson 96/114.7 X 3,033,682 5/1962 Hunt 96/114.7 3,050,391 8/1962 Thompson 96/61 3,598,593 8/1971 Klinger 96/94 3,600,167 8/1971 Judd 96/94 3,326,641 6/1967 Audran et al 23/305 3,415,650 12/1968 Frame et a1 96/94 3,697,271 10/1972 Timson 96/3 OTHER PUBLICATIONS Glafkides, Pierre; Photographic Chemistry; 1958: Fountain Press, London, page 354.

Primary Examiner-J. Travis Brown Assistant Examiner-Alfonso T. Suro Pico Attorney-Robert W. Hampton et al.

[57] ABSTRACT In a process for the preparation of a silver halide photographic emulsion containing a major proportion of chloride, about 0.1 mole to about 5 mole percent of iodide and up to about 10 mole percent of bromide comprising precipitating said silver halide in the presence of a hydrophilic colloid, the improvement which comprises precipitating said silver halide into a medium having a pH in the range 5-9 and a pAg of at least about 7.8 by adding to the precipitation mixture, no later than at the end of said precipitation, a weak solvent for silver halide selected from the group consisting of ammonium chloride, ammonium nitrate and magnesium chloride in a quantity in stoichiometric excess with respect to the quantity of alkali metal chloride necessary for the precipitation of the silver halide, this excess being between 4 moles and 180 moles per 100 moles of formed silver halide.

5 Claims, No Drawings HIGH SPEED SILVER CHLOROIODIDE EMULSIONS BACKGROUND OF THE INVENTION 1, Field of the Invention The present invention relates to a process for the preparation of silver halide photographic emulsions, giving negative images by exposure to a positive original and, more particularly, to a process for the preparation of a silver chloroiodide or silver chlorobromoiodide photographic emulsion, the sensitivity of which is clearly improvedcompared to the usual chloroiodide photographic emulsions.

2. Description of the Prior Art It is well known that silver chloride photographic emulsions have a sensitivity clearly below the sensitivity of the silver bromide or bromoiodide photographic emulsions, so that photographic emulsions containing a large amount of silver chloride are customarily used only for contact printing.

Attempts have been made to increase the sensitivity of silver chloride photographic emulsions, e.g., through the addition of silver halide solvents such as ammonia, but in the majority of cases, the emulsions treated in this way display significant fogging and are practically unusable in photography.

It would, therefore, be desirable to increase the sensitivity of silver chloride or chloroiodide photographic emulsions without increasing the fog level, in order to extend the field of application of these emulsions and to profit from their specific properties, in particular, their great speed of development and fixing, their high covering power, their capability of forming images having a good image tone and their high spectral sensitivity in the ultra-violet, as well as the low reciprocity failure which they present.

The precipitation of silver chloroiodide photographic emulsions in the presence of a quantity of ammonium chloride exceeding the stoichiometric quantity of silver nitrate is described in U. S. Pat. No. 2,401,051, but the silver chloride emulsions described in this patent are precipitated only in media having a pH value of 4.7 or lower. Further, the emulsions that are formed are direct positive photographic emulsions through solarization.

U. S. Pat. No. 3,189,456 describes a process for the preparation of a silver halide photographic emulsion wherein an excess of a water-soluble halide, such as ammonium chloride, is added, but this addition takes place after the precipitation of the silver halide and after a ripening from 5 to 20 minutes at a temperature of from 50C to 70C, and the prepared emulsion is a photodevelopable photographic emulsion.

U. S. Pat. No. 2,696,436 describesa method foraltering the characteristics of an unexposed photographic emulsion coating by immersing the emulsion in a solution of slvernitrate, washing the emulsion, and then immersing the emulsion in a solution of ammonium chloride to convert the silver nitrate to silver chloride, causing the silver chloride in the emulsion to precipitate.

. U. S. Pat. No. 2,618,556 and British Pat. No. 967,524 disclose the addition of ammonium halides to silver halideemulsions to coagulate them.

SUMMARY OF THE INVENTION In accordance with the present invention, it is possible to prepare silver chloriodide or silver chlorobromoidide photographic emulsions which display, in comparison with silver chloroiodide emulsions of the prior art, an increase in sensitivity which may attain l log E when the precipitation of the silver chloroiodide is effected at a pH value close to 8. The silver chloroiodide photographic emulsions of the present invention display a chemical sensitivity which can attain practically the sensitivity of silver bromoiodide photographic emulsions without an appreciable increase in the level of fog, while retaining the great developing and fixing speed which is one of the characteristics of silver chloride emulsions.

The present invention comprises an improvement in a process for the preparation of a silver halide photographic emulsion, containing a major proportion of cloride, about 0.1 mole to about 5 mole percent of iodide and up to about 10 mole percent of bromide, comprising precipitating said silver halide in the presence of a hydrophilic colloid, wherein the improvement comprises precipitating said silver halide into a medium having a pH in the range 5-9 and a pAg of at least about 7.8 by adding to the precipitation mixture, no later than at the end of said precipitation, a weak solvent for silver halide chosen from the group consisting of ammonium chloride, ammonium nitrate and magnesium chloride, in a quantity in stoichiometric excess with respect to the quantity of alkali metal chloride necessary for the precipitation of the silver halide, this excess being between 4 moles and 18 moles per moles of formed silver halide.

As employed herein, the phrase no later than at the end of precipitation is intended to mean that the weak solvent for silver halide can be added to the reaction mixture before the beginning of the precipitation of the silver halide, as, for example, is illustrated in Ex amples 1-13 and 22-25 infra; right at the end of the precipitation of the silver halide, as, for example, is illustrated in Examples 14 and 15, infra or during the precipitation of the silver halide, as, for example, is illustrated in Examples 16-21 infra.

According to one embodiment of the process of the present invention, the weak silver halide solvent, preferably ammonium chloride, is added at the end of the precipitation of the silver chloroiodide emulsion. This embodiment of the process makes it possible to prepare silver chloroiodide or silver chlorobromoiodide emulsions wherein the average size of the grains is smaller, the grain size distribution of the silver halide grains narrower, the contrast factor higher, the level of fog very low and wherein the increase of sensitivity can reach 0.60 log E. However, the increase: of sensitivity of the silver chloroiodide photographic emulsions prepared according to this emodiment of the process is slightly lower than that which can be attained when the weak silver halide solvent is added at the beginning of or during the precipitation of the silver halide.

The process of this invention makes it possible to prepare silver chloroiodide or silver chlorobromoiodide photographic emulsions the sensitivity increase of which, compared with the emulsions prepared in the usual manner, can be adjusted by varying the proper tion of iodide, the quantity of weak solvent for the silver halide and the pH value of the medium for the precipitation of silver halide. In the process of this invention, the solvent power of the precipitation medium for the formed silver halides is maximal when the pH is from 8 to 9, and the solvent power decreases with the pH, but remains practically constant when the pH attains a value between and 7.

It is, therefore, an object of this invention to provide silver chloroiodide or silver chlorobromoiodide photographic emulsions having improved sensitivity.

It is a further object of this invention to provide silver chloroiodide or silver chlorobromoiodide photographic emulsions having improved sensitivity with no increase in the level of fog.

It is a further object of this invention to provide silver chloroiodide or silver chlorobromoiodide photographic emulsions having improved sensitivity with no increase in the level of fog, while retaining the advantages of silver chloride emulsions, particularly, high developing and fixing speed.

It is another object of this'invention to provide a process for the preparation of silver chloroiodide or silver chlorobromoiodide photographic emulsions having improved sensitivity with no increase in the level of fog, while retaining the advantages of silver chloride emulsions, particularly, high developing and fixing speed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the present invention, a weak solvent for silver halide is added to a silver halide precipitation mixture containing a major proportion of chloride.

According to a first embodiment of the process of this invention, ammonium chloride is used, usually a quantity in the range of about 18 to 170 moles, and advantageously a quantity between 45 and 95 moles per 100 moles of silver halide. The ammonium chloride has a certain solvent power with respect to the formed silver halide which increases with the pH value of the precipitation medium. The increase of the sensitivity of the photographic emulsions prepared according to this invention appears to be connected to the solvent power of the ammonium chloride, the maximum sensitivity being capable of reaching 1 log E compared with the silver chloroiodide emulsions prepared by the processes of the prior art. A small quantity of ammonia is liberated in the silver halide precipitation medium since the medium contains ammonium chloride and is basic. This liberated ammonia activates the solvent power of the ammonium chloride but does so without an increase of fog.

According to a second embodiment of the process of this invention, ammonium nitrate is used as the weak solvent for silver halide in an amount advantageously between 0.10 and 1.0 mole per mole of silver halide. It is then necessary to add to the ammonium nitrate a water-soluble chloride, such as sodium chloride, in addition to the chloride necessary for the precipitation, so as to maintain the pAg of the precipitation medium at a value equal to or above 7.8. The molar ratio between the water-soluble chloride and the ammonium nitrate is advantageously between 1/3 and 1/1. Preferably, equimolar amounts of ammonium nitrate and watersoluble chloride are employed.

According to a third embodiment of the process of this invention, magnesium chloride is used as the weak solvent for silver halides.

The silver chloroiodide or silver chlorobromoiodide photographic emulsions prepared according to the invention contain a small portion of iodide and possibly of bromide. The proportion of iodide is between 0.001 and 0.05 mole, advantageously between 0.003 and 0.03 mole, and more particularly, between 0.007 and 0.020 mole per mole of silver halide, but a more extended iodide concentration range can be used. However, if the iodide concentration of the silver halide emulsions prepared according to the invention is below 0.003 mole, the prepared emulsion displays a sizable fog and its sensitivity and contrast factor are reduced, and if the proportion of iodide is above 0.03 mole, the fixing speed of the emulsion so prepared will be considerably reduced with respect to the fixing speed of silver chloride emulsions. The presence of iodide in the silver halide emulsions of this invention makes it possible to increase the sensitivity, the contrast factor and the covering power and to reduce the fog.

The silver chloroiodide photographic emulsions of this invention can contain a small proportion of bromide, e.g., a proportion between 0.02 and 0.10 mole per mole of silver halide. If the proportion of bromide surpasses 0.20 mole, the speeds of development and of fixing are clearly lower than that of the usual silver chloride emulsions.

The preparation of the silver chloriodide or silver chlorobromoiodide emulsions of this invention can be effected by operating at very diversified pH values. Precipitation of the silver chloroiodide emulsion is effected advantageously at a pH value between 5 and 9, the maximum increase of sensitivity being obtained for a pH value equal to approximately 8. However, even when the silver chloroiodide emulsion is precipitated at a pH value of 5, the increase in sensitivity is still 0.55 log E. When the pH value of the precipitation medium increases, the average size of the grains and the level of fog have a tendency to increase.

The process of this invention can be carried out at a pAg value equal to or about 7.8. It is advantageous to employ a constant pAg value during the entire duration of the precipitation of the silver halide.

In order to prepare the silver chloroiodide photographic emulsions of this invention, a solution of sodium chloride or potassium chloride can be reacted with a solution of a water-soluble silver nitrate, in the presence of a small proportion of a water-soluble iodide, such as potassium iodide, and in the presence of the weak solvent for the silver halides, e.g., ammonium chloride. A slight excess of sodium chloride or potassium chloride with respect to the stoichiometric quantity is advantageously employed; this excess can be of from about 0.10 to 0.15 mole for the purpose of increasing the average size of the silver halide grains. The sensitivity and the level of fog will also be slightly increased. Precipitation of the silver chloroiodide emulsion can be effected by any suitable process whatsoever. One can, e.g., operate by a single-jet process, i.e., wherein is introduced, slowly and with stirring, the solution of the water-soluble halides in the aqueous silver nitrate solution or inversely. One can also operate with a two-jet process, e.g., by introducing simultaneously, and with stirring, the aqueous silver nitrate solution and the aqueous sodium chloride solution into an aqueous solution of gelatin which contains potassium iodide and the weak solvent for silver halides, e.g., ammonium chloride. The precipitation of the emulsion is effected at a temperature which is usually between 30C and 75C.

Very diversified hydrophilic colloids can be used as photographic binders for the preparation of silver halide emulsions according to this invention, e.g., gelatin, gelatin derivatives such as those described in French Pat. No. 970,317, colloidal albumin, polysaccharides, cellulose derivatives, synthetic resins, such as polyvinyl compounds, including derivatives of polyvinyl alcohol, acrylamide polymers, etc. The binder of the photographic emulsions can also contain hydrophobic colloids such as aqueous dispersion of vinyl polymers, in particular, polymers which increase the dimensional stability of the photographic products. Examples of these compounds are the water-in-soluble polymers of alkyl acrylates or methacrylates, acrylic acid, sulfoalkyl acrylates or methacrylates, etc.

The silver chloroiodide photographic emulsions precipitated according to the invention are usually submitted to the customary operations of physical and chemical ripening.

The emulsions of this invention may be sensitized with chemical sensitizers, such as with reducing agents; sulfur, selenium or tellurium compounds; gold, platinum or palladium compounds; or combinations of these. Suitable procedures are described in Sheppard et al.,U. S. Pat. No. 1,623,499 issued Apr. 5, 1927; Waller et al., U. S. Pat. No. 2,399,083 issued Apr. 23, 1946; McVeigh U. S. Pat. No. 3,297,446 issued Jan. 10, 1967. See also French Pat. Nos. 599,934; 983,991; 1,053,787; 1,053,786; 1,006,813; 949,227 and 942,831.

The usual photographic addenda can be added to the emulsions of this invention. For example, they can contain plasticizers and lubricants such as polyalcohols, e.g., glycerin anddiols of the type described in Milton et a], U. S. Pat No. 2,960,404 issued Nov. 1, 1966; fatty acids or esters such as those described in Robijns U. S. PaLNo. 2,588,765 issued Apr. 11, 1964; and silicone resins such as those described in DuPont British Pat. No. 955,061 issued Apr. 15, 1964.

The emulsions of this invention can contain surfactants such as saponin; anionic compounds such as the alkyl aryl sulfonates described in Baldsiefen U. S. Pat. No. 2,600,831 issued June 17, 1952; amphoteric compounds such'as those described in Ben-Ezra U. S. Pat. No. 3,133,816 issued May 19, 1964; and water soluble adducts of glycidol. and an alkyl phenol such as those described in Olin Mathieson British Pat. No. 1,022,878 issued. Mar. 16, 1966; and Knox U. S. Pat. No. 3,514,293 issuedMay 26, 1970.

The silver halide emulsions used in the practice of this invention can be protected against the production of fog and can be stabilized against loss of sensitivity during. keeping. Suitable antifoggants and stabilizers eachused alone or in combination include thiazolium salts described in Brooker et al., U. S. Pat. No. 2,131,038 issued Sept. 27, 1938; and Allen et al., U. S. Pat. No. 2,694,716 issued Nov. 16, 1954; the azaindenes' described in Piper U. S. Pat. No. 2,886,437 issuedMay 12, 1959; and l-leimbach et al., U. S. Pat. No. 2,444,605 issued July 6, 1948; the mercury salts as described in Allen et al., U. S. Pat. No. 2,728,663 issued Dec. 27, 1955; the urazoles described in Anderson et al., U.S.Pat. No. 3,287,135 issued Nov. 22, 1966; the sulfocatechols described. in Kennard et al., U. S. Pat. No.. 3,236,652 issuedFeb. 22, 1966; the oximes described in Carroll et al., British Pat. No. 623,448 issued May 18, 1949; nitron; nitroindazoles; the mercaptotetrazoles described in Kennard et al., U. S. Pat. No. 3,266,897 issued Aug. 16, 1966; and Luckey et al., U. S. Pat. No. 3,397,987 issued Aug. 20, 1968; the polyvalent metal salts described in Jones U. S. Pat. No. 2,839,405 issued June 17, 1958; the thiuronium salts described in Herz et al., U. S. Pat. No. 3,220,839 issued Nov. 30, 1965; the palladium, platinum and gold salts described in Trivelli et al., U. S. Pat. No. 2,566,263 issued Aug. 28, 1951; and Yutzy et al., U. S. Pat. No. 2,597,915 issued May 27, 1952.

Various organic or inorganic hardeners, alone or in combination, such as the aldehydes, and blocked aldehydes as described in Allen et al., U. S. Pat. No. 3,232,764 issued Feb. 1, 1966, ketones, carboxylic and carbonic acid derivatives, sulfonate esters, sulfonyl halides and vinyl sulfonyl ethers as described in Burness et al., U. S. Pat. No. 3,539,644 issued Nov. 10, 1970, active halogen compounds, epoxy compounds, aziridines, active olefins, isocyanates, carbodiimides, polymeric hardeners such as oxidized polysaccharides like dialdehyde starch and oxyguargum and the like can be employed in combination with the emulsions of this invention.

Spectral sensitizing dyes can be used convenientlyto confer additional sensitivity to the light sensitive silver halide emulsions of this invention. For instance, additional spectral sensitization can be obtained by treating the emulsion with a solution of a sensitizing dye in an organic solvent or the dye may be added in the form of a dispersion as described in Owens et al., British Pat. No. 1,154,781 issued June 11, 1969. For optimum results, the dye may either be added to the emulsion as a final step or at some earlier stage. The aforementioned additives can be added to the emulsions either before or after the sensitizing dyes.

Sensitizing dyes useful in sensitizing these emulsions are described, for example, in Brooker et al., U. S. Pat. No. 2,526,632 issued Oct. 24, 1950; Sprague U. S. Pat. No. 2,503,776 issued Apr. 11, 1950; Brooker eta1., U. S. Pat. No. 2,493,748 issued Jan. 10, 1950; and Taber et al., U. S. Pat. No. 3,384,486 issued May 21, 1968. Spectral sensitizers which can be used include the cyanines, merocyanines, complex (trior tetranuclear) merocyanines, complex (trior tetranuclear) cyanines, holopolar cyanines, styryls, hemicyanines (e.g., enamine hemicyanines), oxonols and hemioxonols.

Dyes of the cyanine classes may contain such basic nuclei as the thiazolines, oxazolines, pyrrolines, pyridines, oxazoles, thiazoles, selenazoles and imidazole. Such nuclei may contain alkyl, alkylene, hydroxyalkyl, sulfoalkyl, carboxyalkyl, aminoalkyl and enamine groups and may be fused to carbocyclic or heterocyclic ring systems either unsubstituted or substituted with halogen, phenyl, alkyl, haloalkyl, cyano, or alkoxy groups. The dyes may be symmetrical or unsymmetrical and may contain alkyl, phenyl, enamine or heterocyclic substituents on the methine or polymethine chain.

The merocyanine dyes may contain the basic nuclei mentioned above as well as acid nuclei such as thiohydantoins, rhodanines, oxazolidenediones, thiazolidenediones, barbituric acids, thiazolineones, and malononitrile. These acid nuclei may be substituted with alkyl, alkylene, phenyl, carboxyalkyl, sulfoalkyl, hydroxyalkyl, alkoxyalkyl, alkylamino groups, or heterocyclic nuclei. Combinations of these dyes may be used, if desired. In addition, supersensitizing addenda which do not absorb visible light may be included, for instance, ascorbic acid derivatives, azaindenes, cadmium salts, and organic sulfonic acids as described in McFall et al., U. S. Pat. No. 2,933,390 issued Apr. 19, 1960; and Jones et al., U. S. Pat. No. 2,937,089 issued May 17, 1960.

Developing agents such as hydroquinones, catechols, aminophenols, 3-pyrazolidones, ascorbic acid and its derivatives, reductones and phenylenediamines can be used in the practice of this invention. Combinations of developing agents can be employed in the practice of the invention. The developing agents can be in a silver halide emulsion and/or in another suitable location in the photographic element. The developing agents may be added from suitable solvents or in the form of dispersions as described in Yackel U. S. Pat. No. 2,592,368 issued Apr. 8, 1952; and Dunn et al., French Pat. No. 1,505,778.

The silver halide photographic emulsions of the present invention can be coated on a wide variety of supports. Typical supports include cellulose nitrate film, cellulose ester film, poly(vinyl acetal) film, polystyrene film, poly (ethylene terephthalate) film, polycarbonate film and related films or resinous materials, as well as glass, paper, metal and the like. Typically, a flexible support is employed, especially a paper support, which can be partially acetylated or coated with baryta and/or an alpha-olefin polymer, particularly a polymer of an alpha-olefin containing two to 10 carbon atoms such as polyethylene, polypropylene, ethylenebutene copolymers and the like.

The silver chloroiodide photographic emulsions precipitated according to this invention can be used in a great number of applications, in particular in medical and industrial radiography. In such applications, it is useful to obtain rapidly stable images and, by virtue of the great developing and fixing speed of the silver chloride emulsions of this invention, it is possible to attain a satisfactory sensitivity. The silver chloroiodide photographic emulsions precipitated according to this invention can also be employed to effect recordings at very high speeds or recordings in very short exposure times (10's) which require a rapid development. One can, e.g., use such photographic emulsions for the preparation of fast development photographic papers, for recording or for photocomposition. These emulsions can also be used in the field of graphic arts, but they are particularly useful in medical radiography without screen and in industrial radiography, when rapid treatment is desired. Radiography products which contain-an emulsion of this invention can be used in automatic processing machines, for example, the rapid-access Kodak X-Omat M6 machines, wherein the entire duration of treatment does not surpass l minute and seconds. This is contrary to the radiography products of the prior art which contain silver bromoiodide emulsions the speed of treatment of which is much slower and which require a treatment, in automatic machines, of a duration of usually between 6 minutes and 12 minutes, in order to obtain stable images for storage.

The photographic products which contain emulsions that are prepared according to this invention can be treated by means of any usual photographic treatment whatsoever, but it is advantageous to employ developing and fixing baths with rapid action so as to profit to the maximum from the great developing speed of these silver chloride emulsions.

The following examples are included for a further understanding of the invention.

Examples 1 to 13 illustrate an embodiment of the process of this invention wherein the weak solvent for silver halide is added to the reaction mixture before the beginning of the precipitation of the silver halides.

EXAMPLE 1 The following four solutions are prepared:

-Solution A Silver Nitrate 170 g Mercuric Chloride 0.045 mg Water 900 ml Solution B Sodium Chloride 67 g Water 900 ml A sufficient quantity of a sodium hydroxide solution to obtain a pH value of 8. Solution c Gelatin derivative described in 27 g French Pat. No. 970,3l7 Water 700 ml Ammonium Chloride 25 g Sufficient sodium hydroxide to obtain pH 8. Potassium lodide l.8 g Water-sufficient quantity to obtain 900 ml Solution D Gelatin 45 g Water 540 ml Solutions A and B are maintained at 50C and Solution C at 65C.

Solution C is introduced into the precipitation vessel. Solutions A and B are added simultaneously while slowly stirring over a period of approximately 20 minutes, Solution B having a 30second advantage over Solution A.

At the end of the precipitation, the reaction medium is cooled to 35C and the water-soluble salts are separated by means of coagulation and decantation of the supernatant liquid. The emulsion that is precipitated is coagulated by adjusting the pH value of the reaction medium to 3.5 with an 8N sulfuric acid solution.

Solution D is then added and then the pH value is adjusted to 4.5 with 2N sulfuric acid solution. The temperature is maintained at 40C for 5 minutes.

9.6 mg of aurous sulfide is added as a chemical sensitizer and 5 2.8 mg of 4-hydroxy-6-methyltetrazaindene as a fog inhibitor. The temperature of the medium is raised to 70C and maintained at this temperature for 5 minutes, whereupon it is cooled to 40C. A mixture of /25 (vol.) water/methanol containing g. per liter of saponin is prepared and 5 ml of this mixture is added to the emulsion. Then from 3 ml to 5 ml of a 26.6 g. per liter mucochloric acid solution is added and, finally, a sufficient quantity of distilled water is added so as to obtain a total mass of 1,000 g. The different solutions are heated and cooled in such a way that the variation of temperature is 1.5C per minute.

The emulsion thus prepared is applied to a polyethylene terephthalate support in the amount of 60 mg/dm. The photosensitive film is dried and exposed under the usual exposure conditions for a very short exposure time (l0' s).

Development is then carried out in a developer having the following composition:

Sodium metabisulfite 30 g 0.40 potassium hydroxide solution 50 g Borax 5 g l-phenyl-3-pyrazolidone 0.75 g Hydroquinone l5 g Sodium fluoride 0.6 g Potassium bromide 4 g Potassium iodide 0.025 g 5-methyl-l,2,3-benzotriazole 0.020 g d-phenylmercaptotetrazole 0.006 g sequestering agent (sodium salt of 0.4 g ethylenediaminetetraacetic acid) Water sufficient quantity to obtain ll.

The pH is adjusted to 10.40

Development is carried out at 20C for 3 minutes. The developed film is then fixed in a sodium thiosulfate fixing bath, washed and dried.

As a comparison, a test sample is made with an emulsion prepared in the absence of ammonium chloride.

The sensitometric results are shown in Table l of Example 4.

EXAMPLE 2 Example 1 is repeated except the precipitation of the emulsion is carried out at a pH of 5. The sensitometric results are shown in Table I of Example 4.

EXAMPLE 3 Example 1 is repeated except that the very short exposure time is replaced with a radiography exposure of 80 kV. The sensitometric results are shown in Table I of Example 4.

EXAMPLE 4 Example 2 is repeated except that the very short exposure time is replaced with the radiographic exposure of Example 3. The results are shown in Table I.

TABLE I Ex. pH value of the Mode of Relative precipitation mix. Exposure Sensitivity test sample Short Exp. (w/o NH CI) 5 time (10"s) 100 l 8 id 360 2 5 id 200 test sample Radiography (w/o NH CI) 5. Exposure I 3 8 460 4 5 id 240 EXAMPLES 5 8 Example 1 is repeated except that a quantity of ammonium chloride equal to 50 g per mole of formed silver halide is employed and the precipitation of the silverhalide is carried out at pH values of 5, 7, 8, 9 and 10 respectively. The relative sensitivity of the emulsions is determined and the results are shown in Table TABLE II Ex. pH value of the Mode of Relative precipitation mix. Exposure Sensitivity Test sample Short time of (w/o NH CI) 5 ex. (10s) lOO 5 5 id 360 TABLE ll-Continued Ex. pH value of the Mode of Relative precipitation mix. Exposure Sensitivity 7 8 id 790 8 9 id 790 l0 id fogged emulsion It is noted that the maximum sensitivity is obtained for a pH value of the precipitation medium of the silver halide between 8 and 9, and that, when the pH value is 10, the emulsion no longer displays sensitivity. The relative sensitivity of the emulsion test sample that is precipitated in the absence of ammonium chloride is equal to when the pH value of the precipitation medium is 5 and is no longer measurable for pH values between 7 and 10 because of the high level of fog.

EXAMPLES 9 AND 10 Example 1 (very short exposure time) is repeated, but the quantity of ammonium chloride (in g/mole of formed silver halides) is varied from 25 g to 100 g and the precipitation of the silver halide is carried at a pH of 5. The relative sensitivities of the emulsions are shown in Table III.

TABLE III (Short time of exposure) l0 s Relative Ex. pH value of Ammonium precipitation chloride (g/mole Sensitivity mixture of silver halide) Test sample 5 L 310 5 I00 (fogged emulsion) EXAMPLES ll AND 12 Examples 9 and 10 are repeated except that radiographic exposure is substituted for the very short time of exposure. The relative sensitivities of the emulsions are shown in Table IV.

One operates as in Example 3 (radiographic exposure) but by replacing the developing bath used in that example, in a discontinuous process, with developing baths used in the automatic Kodak X-Omat M6 processing machine which comprise the following solutions:

Solution A 45/l00 potassium sulfite solution 130.5 g Hydroquinone 30 g Potassium Carbonate l0 sequestering agent (disodium l g salt of ethylenediaminetetraacetic acid) Sodium Carbonate 4.3 g

S-methyl-l,2,3-benzotriazole 0.060 g Diethyleneglycol l4 g 0.35 potassium hydroxide 32.6 g solution 1 5 Solution B Crystallizable Acetic Acid 16.87 g l-phenyl-3-pyrazolidone 1.5 g S-nitroindazole 0.25 Diethyleneglycol l8.27 g Solution C 0.25 glutaraldehyde solution l9.72 g Sodium metabisulfite 3.75 g Crystallizable Acetic Acid 0.25 g

The Kodak X-Omat processing machine uses an ordi- 2 5 nary sodium thiosulfate fixing bath. The entire duration of the treatment is 1 minute and seconds at 36C. The treated products are thoroughly dried and the images thus obtained are stable in storage.

If a test sample is made with a radiographic product 30 of the prior art, which contains a usual silver bromoiodide emulsion which, after radiographic exposure, is treated in the Kodak X-Omat M6 machine, one obtains, at the exit of the machine, a film that is not entirely dry and which retains too large a quantity of sodium thiosulfate, the radiographic image thus obtained not being stable in storage.

The following examples illustrate an embodiment of the process of this invention wherein ammonium chloride is added after precipitation of the silver halide.

EXAMPLE 14 Example 1 is repeated but the ammonium chloride of Solution C is omitted and 43 g. of ammonium chloride is added right at the end of the precipitation of the sil ver halide. The emulsion thus prepared displays a relative sensitivity equal to 350 (short time of exposure) compared with a test sample that is precipitated in the absence of ammonium chloride, the relative sensitivity of which is 100.

EXAMPLE 15 EXAMPLE 16 The following solutions are prepared:

Solution A Silver Nitrate 170 g Water 900 ml -Continued Solution A Solution B Sodium Chloride 49 g Sodium Bromide 10 g Water 900 ml Solution B Ammonium Chloride 26 g Mercuric Chloride 0.045 mg Water ml Solution C Gelatin derivative described in French 27 g Pat. No. 970,317 Water 700 ml Sodium Chloride 5.6 g Potassium Iodide 1.8 g Water-sufficient to obtain 900 ml The pH of Solutions B, B and C is adjusted to 8. Solution C is introduced into a precipitation vessel, then slowly and simultaneously, Solutions A and B are added, the rates of addition being adjusted for a total duration of 20 minutes. At the fifth minute of precipitation, Solution B is added rapidly whereupon the pH of the precipitation medium is adjusted to 8. Then the addition of Solutions A and B is continued and then one operates as in Example 1 (short exposure time).

The emulsion thus prepared displays a relative sensitivity equal to 250 compared with a sample emulsion that is precipitated in the absence of ammonium chloride, the relative sensitivity of which is equal to l00.

EXAMPLE 17 Example 16 is repeated but radiographic exposure is used in place of the short time of exposure.

The emulsion thus prepared displays a relative sensitivity equal to 200.

EXAMPLE 18 Example 16 is repeated but the precipitation is effected at pH 5. The relative sensitivity of the photographic emulsion thus prepared is 200 (short time of exposure).

EXAMPLE l9 Example 17 is repeated but the precipitation is effected at a pH of 5. The relative sensitivity of the photographic emulsion thus prepared is (radiographic exposure).

EXAMPLE 20 Examples 16 and 17 are repeated except that into Solution C is introduced a quantity of potassium iodide equal to 4.9 g instead of 1.8 g. The photographic emulsions thus prepared display a relative sensitivity equal to 310 (short time of exposure) and 250 (radiographic exposure) respectively.

EXAMPLE 21 Example 20 is repeated except the precipitation is effected at a pH OF 5. The emulsions thus prepared display a relative sensitivity equal to 250 (short time of exposure) and 200 (radiographic exposure) respectively.

Examples 22 and 23 illustrate the utilization of ammonium nitrate as the weak solvent for silver halide.

EXAMPLE 22 EXAMPLE 23 Example 22 is repeated except the short time of exposure is replaced by radiographic exposure. The relative sensitivity of the emulsion is 300.

Examples 24 and 25 illustrate the utilization of magnesium chloride as the weak solvent for silver halide.

EXAMPLE 24 Example 22 is repeated except the mixture of ammonium nitrate and sodium chloride is replaced by magnesium chloride (95g, i.e., 1 mole per mole of silver halide). The relative sensitivity of the emulsion is 360.

EXAMPLE 25 Example 24 is repeated except the short time of exposure is replaced by radiographic exposure. The relative sensitivity of the emulsion is 280.

The invention has been described in detail with par ticular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the iav ntiqns.

1th.?! is slaimeiisam 1. In a process for the preparation of a silver chloroiodide or chlorobromoiodide photographic emulsion containing a major proportion of chloride, about 0.1 mole to about mole percent of iodide and up to about lomole p tq ntef remids mp isin sp ssitzitat said silver chloroiodide or chlorobromoiodide in the presence of a hydrophilic colloid, the improvement which comprises precipitating said silver chloroiodide or chlorobromoiodide into a medium having a pH in the range 8-9 and a pAg of at least about 7.8 by adding to the precipitation mixture, no later than at the end of said precipitation, between 4 moles and 180 moles of ammonium chloride, ammonium nitrate or magnesium chloride for every 100 moles of the final silver halide product.

2. The process of claim 1 wherein the silver chloroiodide or silver chlorobromoiodide emulsion contains a proportion of iodide between about 0.003 and 0.03 mole per mole of silver chloroiodide or silver chlorobIQtaQiQQ Qe.

3. The process of claim 1 wherein the ammonium chloride, ammonium nitrate or magnesium chloride is added to the precipitation vessel before the beginning of the precipitation reaction.

4. The process of claim 1 wherein between about 45 moles and moles of ammonium chloride is employed f( r every moles of the final silver halide prqdygt.

5. In a process for the preparation of a silver chloroiodide or chlorobromoiodide photographic emulsion containing a major proportion of chloride, about 0.1 mole to about 5 mole percent of iodide and up to about 10 mole percent of bromide comprising precipitating said silver chloroiodide or chlorobromoiodide in the presence of a hydrophilic colloid, the improvement which comprises precipitating said silver chloroiodide or chlorobromoiodide into a medium having a pH in the range 8-9 and a pAg of at least about 7.8 by adding between 45 moles and 95 moles of ammonium chloride for every 100 moles of the final silver halide product to the precipitation vessel before the beginning of the presieitat asmstat a..- 

2. The process of claim 1 wherein the silver chloroiodide or silver chlorobromoiodide emulsion contains a proportion of iodide between about 0.003 and 0.03 mole per mole of silver chloroiodide or silver chlorobromoiodide.
 3. The process of claim 1 wherein the ammonium chloride, ammonium nitrate or magnesium chloride is added to the precipitation vessel before the beginning of the precipitation reaction.
 4. The process of claim 1 wherein between about 45 moles and 95 moles of ammonium chloride is employed for every 100 moles of the final silver halide product.
 5. In a process for the preparation of a silver chloroiodide or chlorobromoiodide photographic emulsion containing a major proportion of chloride, about 0.1 mole to about 5 mole percent of iodide and up to about 10 mole percent of bromide comprising precipitating said silver chloroiodide or chlorobromoiodide in the presence of a hydrophilic colloid, the improvement which comprises precipitating said silver chloroiodide or chlorobromoiodide into a medium having a pH in the range 8-9 and a pAg of at least about 7.8 by adding between 45 moles and 95 moles of ammonium chloride for every 100 moles of the final silver halide product to the precipitation vessel before the beginning of the precipitation operation. 